Push and Pull Premix Combustion System With Blocked Vent Safety Shutoff

ABSTRACT

A furnace with a push and pull combustion system is disclosed. The furnace may include a cabinet housing a burner box, a gas valve assembly, a premix chamber, a heat exchanger, a blower, an induced-draft blower, and a flue pipe. The gas valve assembly may meter gas into the premix chamber, while the blower may draw air into the premix chamber, wherein air and gas may mix to produce a lean gas/air mixture. The blower may also push the lean gas/air mixture into the burner box. The burner box may ignite the lean gas/air mixture to produce combustion products. A blocked vent safety shutoff switch may be mounted over an opening of the burner box to ensure negative pressure by detecting any leakage of combustion products. The induced-draft blower may pull the combustion products through the heat exchanger, the flue pipe, and out into the atmosphere.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to furnaces and, in particular,relates to a push and pull premix combustion system with blocked ventsafety shutoff in a furnace.

BACKGROUND OF THE DISCLOSURE

Gas furnaces are widely installed in homes for heating purposes.Furnaces contain a burner box wherein a mixture of gas and air areburned, creating hot gaseous products of combustion. One common type offurnace is an induced-draft gas furnace. In an induced-draft gasfurnace, a gas valve typically establishes the flow of gas to theburners while a motor-controlled blower induces air for combustion bycreating a negative pressure. Within the burner box, air and gas aremixed and ignited by an igniter, creating hot gaseous combustionproducts. Negative pressure is important for the furnace to operatesafely. The negative pressure created by the induced-draft blowerensures that the gaseous combustion products are pulled through a heatexchanger and then pushed out of the home through a sealed vent system.In instances where the induced-draft blower may be operatingineffectively by not inducing enough air, an inappropriate air to gasmixture may occur reducing the designed in negative pressure andpotentially allowing the furnace to emit combustion gases into the home.Combustion emission, also referred to as NO emission, is of increasingconcern due to the health hazard and atmospheric pollution it creates.Moreover, regulations are mandating stricter emission limitations. Aneed for a lean gas/air mixture is thus in demand.

A known technique for achieving gas-lean operation is to premix the gaswith air before burning it. Such premixing allows the gas and airmixture to burn cooler, reducing NO_(x) production. A drawback topremixing the gas and air is that it increases the quantity ofcombustible mixture. Thus, increasing the potential for flame flashback, auto ignition, and detonation if positive pressures propagate intothe burner box. Such hazards are unacceptable. Thus, a need for agas-lean operating furnace that ensures negative pressure operationstill remains.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the disclosure, a push and pullcombustion system for a furnace is disclosed. The push and pullcombustion system may include a premix chamber, a gas valve assembly, ablower, a burner box, and an induced-draft blower. The premix chambermay mix gas and air to produce a lean gas/air mixture. The gas valveassembly, coupled to the premix chamber, may meter gas into the premixchamber. The burner box, downstream of the premix chamber, may have anigniter which may ignite the lean gas/air mixture to produce combustionproducts. The blower, coupled to the premix chamber, may draw air intothe premix chamber. The blower may also push the lean gas/air mixtureinto the burner box. The induced-draft blower may pull the combustionproducts out of the burner box.

In accordance with another aspect of the disclosure, a furnace with apush and pull combustion system is disclosed. The furnace may include acabinet housing therein a burner box, a gas valve assembly, a premixchamber, a heat exchanger, a blower, an induced-draft blower, and a fluepipe. The premix chamber may mix gas and air to produce a lean gas/airmixture. The gas valve assembly, coupled to the premix chamber, maymeter gas into the premix chamber. The burner box, downstream of thepremix chamber, may have an igniter which may ignite the lean gas/airmixture to produce combustion products. The blower, coupled to thepremix chamber, may draw air into the premix chamber, wherein air andgas may mix to produce a lean gas/air mixture. The blower may also pushthe lean gas/air mixture into the burner box. The heat exchanger may bedownstream of the burner box. The flue pipe may be downstream of theheat exchanger. The induced-draft blower, coupled in-between the fluepipe and the heat exchanger, may pull the combustion products throughthe heat exchanger, then push the combustion products through the fluepipe, and out into the atmosphere.

In accordance with yet another aspect of the disclosure, a method forcontrolling combustion emission for a furnace is disclosed. The methodmay include metering gas into a premix chamber, drawing air into thepremix chamber, mixing gas and air within the premix chamber to producea lean gas/air mixture, pushing the lean gas/air mixture into a burnerbox, igniting the lean gas/air mixture within the burner box to producecombustion products, and pulling the combustion products out of theburner box.

Other advantages and features will be apparent from the followingdetailed description when read in conjunction with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed system and method,reference should be made to the embodiments illustrated in greaterdetail in the accompanying drawings, wherein:

FIG. 1 is a block diagram of an embodiment of a furnace with a pullcombustion system constructed in accordance with the teachings of theprior art;

FIG. 2 is a front perspective view of an embodiment of a furnace with apull combustion system constructed in accordance with the teachings ofthe prior art;

FIG. 3 is a block diagram of an embodiment of a furnace with a push andpull premix combustion system constructed in accordance with theteachings of the present disclosure;

FIG. 4 is a front perspective view of an embodiment of a furnace with apush and pull premix combustion system constructed in accordance withthe teachings of the present disclosure;

FIG. 5 is a perspective view of an embodiment of a furnace with anexploded view of a push and pull premix combustion system constructed inaccordance with the teachings of the present disclosure;

FIG. 6 is a block diagram of a second embodiment of a furnace with apush and pull premix combustion system constructed in accordance withthe teachings of the present disclosure;

FIG. 7 is a partial perspective view of a furnace with a blocked ventsafety shutoff coupled to a push and pull premix combustion systemconstructed in accordance with the teachings of the present disclosure.

It should be understood that the drawings are not necessarily to scaleand that the disclosed embodiments are sometimes illustrateddiagrammatically and in partial views. In certain instances, detailswhich are not necessary for an understanding of the disclosed methodsand systems or which render other details difficult to perceive may havebeen omitted. It should be understood, of course, that this disclosureis not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

In FIGS. 1 and 2, a furnace 100 with a pull combustion system which maybe operated according to the principles of the prior art is illustrated.Pull combustion systems operate with negative pressure throughout thecombustion system, wherein air and gas are pulled into a burner box forcombustion, and then upon ignition, combustion products may be pulledout of the burner box. Induced-draft furnaces commonly utilize a pullcombustion system. The induced-draft furnace 100 may include a cabinet102, housing therein a burner box 104, a gas valve assembly 106, a heatexchanger 108, an induced-draft blower 110, and a circulating air blower112. In operation, gas valve assembly 106 may meter the flow of gas 114through a gas manifold 116, through a burner tube 118, and into theburner box 104. Simultaneously, the induced-draft blower 110 may pullatmospheric air 120 from an air inlet 122 of the burner tube 118 intothe burner box 104, wherein air 120 and gas 114 may be mixed and thenignited by an igniter 124. A flame sensor 126 housed in the burner box104 may ensure that combustion successfully occurs and a flame 128 maybe present. Hot gaseous combustion products 130 may then be drawnthrough the heat exchanger 108 by the induced-draft blower 110 andexpelled through a flue pipe 132, out of the home, and into theatmosphere. As the hot gaseous combustion products 130 flow through theheat exchanger 108, air 134 may be heated as it blows across the heatexchanger 108, circulated through the air ducts (not shown), anddirected back into home by the circulating air blower 112.

As stated above, premixing gas and air prior to combustion may ensure aleaner gas/air mixture and thus lower NO emission. However, in the eventthe induced-draft blower 110 may be operating ineffectively, i.e.inefficient air to gas mixture may occur, excessive NO emission may beproduced and expelled into the atmosphere or even the home, in the eventthe flue pipe 132 may be clogged. In FIGS. 3-5, the present disclosuretherefore provides a furnace 200 with a push and pull premix combustionsystem. The following description may be made with reference to afurnace 200, but it should be understood that the present disclosurecontemplates incorporating a push and pull premix combustion system witha water heater, boiler, or any other type of unit capable of combustion.

Referring now to FIGS. 3 and 4, a furnace 200 may include a cabinet 202,housing therein a burner box 204, a gas valve assembly 206, a heatexchanger 208, an induced-draft blower 210, a circulating air blower212, and a premix chamber 235 housing within it, a premix blower 236with a premix blower motor 238. In operation, gas valve assembly 206 maymeter the flow of gas 214 into the premix chamber 235, while atmosphericair 220 may be drawn into the premix chamber 235 by the premix blowermotor 238. The premix blower 236 may mix gas 214 and air 220 and maypush a lean gas/air mixture 240 through a gas manifold 216, past a flowtuning screen 242 and a burner mixing tube 244, and into the burner box204. Within the burner box 204, the lean gas/air mixture 240 may beignited by an igniter 224. A flame sensor 226 housed in the burner box204 may ensure that a combustion successfully occurred and a flame 228may be present. Hot gaseous combustion products 230 may then be pulledthrough the heat exchanger 208 by the induced-draft blower 210 andexpelled through a flue pipe 232, out of the home, and into theatmosphere. As the hot gaseous combustion products 230 flow through theheat exchanger 208, air 234 may be heated as it blows across the heatexchanger 108, circulated through the air ducts (not shown), anddirected back into home by the circulating air blower 212.

Referring now to FIG. 5, an exploded view of the push and pull premixcombustion system in furnace 200 is illustrated. The gas valve assembly206 may be coupled to the premix chamber 235, housing within it, thepremix blower 236 and the premix blower motor 238. The premix blowermotor 238 may be coupled to the premix blower 236. The premix chamber235 may be coupled to the gas manifold 216. The gas manifold 216 may becoupled to the burner mixing tubes 244 with at least one flow tuningscreen 242 in between each burner mixing tube 244 and gas manifoldoutlet 216 a. Mixing tube adapters 246 may mount the burner mixing tubes244 to the burner box 204. The flame sensors 226 and igniters 224 may beaccommodated by the burner box 204. The burner box 204 also may housepremix burners 248, which may be mounted onto the burner box 204. A cellpanel adaptor bracket 250 may mount the burner box 204 to the furnace200.

In FIG. 6, another exemplary embodiment of a furnace 300, similar tofurnace 200 is disclosed. The furnace 300 may operate similarly tofurnace 200 with at least one exception. Instead of gas 214 and air 220being premixed in the premix chamber 235, as depicted with furnace 200,gas 314 and air 320 may be premixed within a burner mixing tube 344 infurnace 300. In operation, gas valve assembly 306 may meter the flow ofgas 314 through a gas manifold 316 and into the burner mixing tube 344.Simultaneously, an air blower 352 may draw atmospheric air 320 into theburner mixing tube 344, wherein air 320 and gas 314 may be mixed. Withinburner mixing tube 344, a lean gas/air mixture 340 may then be pushed bythe air blower 352 into the burner box 304, wherein it may be ignited byan igniter 324. A flame sensor 326 housed in the burner box 304 mayensure that a combustion successfully occurred and a flame 328 may bepresent. Hot gaseous combustion products 330 may then be pulled throughthe heat exchanger 308 by the induced-draft blower 310 and expelledthrough a flue pipe 332, out of the home, and into the atmosphere. Asthe hot gaseous combustion products 330 flow through the heat exchanger308, air 334 may be heated as it blows across the heat exchanger 308,circulated through the air ducts (not shown), and directed back intohome by the circulating air blower 312.

In FIGS. 3-6, as the lean gas/air mixture 240, 340 is pushed into theburner box 204, 304, a positive pressure may start to accumulate in theburner box 204, 304, and may leak into the heat exchanger 208, 308. If apositive pressure is formed in the heat exchanger 208, 308, any breachin the heat exchanger 208, 308 may result in combustion products leakingout of the heat exchanger 208, 308 and into the home air 234, 334. Toavoid this, the positive pressure may be negated by the greater negativepressure created in the burner box 204, 304 by the pulling-effect of theinduced-draft blower 210, 310. The negative pressure may ensure that anybreach in the heat exchanger 208, 308 would not result in combustionproducts leaking out of the heat exchanger 208, 308, and into the homeair 234, 334.

Another feature of the present disclosure may be reduced harmonics oracoustics, making the unit relatively quiet to operate. By way ofbackground it is important to understand that as the positive pressurefrom upstream collides with the negative pressure from downstream,combustion resonance may occur in the burner box 204, 304. To reducethis combustion oscillation, openings 254, 354 in the burner box 204,304 may allow the burner box 204, 304 to communicate with atmosphericpressure, thus decoupling the upstream and downstream acoustic paths.With the upstream and downstream paths decoupled, the two paths may nolonger react to each other during combustion, thus eliminatingcombustion resonance and lowering sounds emitted by the furnace 200,300. In one exemplary embodiment, the size of the opening 254, 354relative to the volume of the burner box 204, 304 may determine theeffectiveness of the decoupling.

Furthermore, in the event that positive pressure exceeds negativepressure in the burner box 204, 304, the gas valve assembly 206, 306 maybe shutoff as a safety precaution. In one exemplary embodiment, positivepressure may exceed negative pressure if an imbalance in push versuspull occurs due to, but not limited to, the induced-draft blower 210,310 operating ineffectively or malfunctioning, and/or the heat exchanger208, 308 or the flue pipe 232, 332 being clogged. In FIGS. 3, 6, and 7,a blocked vent safety shutoff (BVSS) housing 256, 356 may be mountedover the opening 254, 354 of the burner box 204, 304 in such a manner soas not to block the opening 254, 354. The BVSS housing 256, 356 includesan opening 256 a, 356 a which may be aligned with the opening 254, 354on the burner box 204, 304. A thermal switch 258, 358 may be coupled tothe BVSS housing 256, 356. It is to be understood that any other type ofa temperature sensor, besides the thermal switch 258, 358, may beincorporated herein. As positive pressure exceeds negative pressure inthe burner box 204, 304, hot gaseous combustion products 230, 330 mayseep out of the opening 254, 354, making thermal contact with thethermal switch 258, 358. Once the temperature of the outwardly flowinghot gaseous combustion products 230, 330 reaches a specific level, abimetal element (not shown) in the thermal switch 258, 358 may open andshutoff the gas valve assembly 206, 306.

In one exemplary embodiment, the thermal switch 258, 358 may be anauto-resettable thermal switch with an algorithm as described in detailin U.S. Pat. No. 6,851,948, owned by the assignee of the presentdisclosure and the disclosure of which is incorporated herein byreference in its entirety. The auto-resettable thermal switch indisclosure '948 is capable of resetting itself, i.e. closing the bimetalelement in the thermal switch, automatically. Furthermore, the algorithmin disclosure '948 ensures a self-recovery method without a significantincrease in combustion product emissions into a given space.

While only certain embodiments have been set forth, alternatives andmodifications will be apparent from the above description to thoseskilled in the art. These and other alternatives are consideredequivalents and within the spirit and scope of this disclosure and theappended claims.

1) A push and pull combustion system for a furnace, comprising: a premixchamber capable of mixing gas and air to produce a lean gas/air mixture;a gas valve assembly coupled to the premix chamber and capable ofmetering gas into the premix chamber; a burner box downstream of thepremix chamber; a blower coupled to the premix chamber and capable ofdrawing air into the premix chamber, and pushing the lean gas/airmixture into the burner box; an igniter associated with the burner boxcapable of igniting the lean gas/air mixture to produce combustionproducts; and an induced-draft blower capable of pulling the combustionproducts out of the burner box. 2) The push and pull combustion systemof claim 1, wherein the burner box includes an opening and a blockedvent safety shutoff switch is mounted over the opening, the blocked ventsafety shutoff switch adapted to make thermal contact with fluid flowingout of the opening, and sense leakage of combustion products out of theburner box. 3) The push and pull combustion system of claim 2, whereinthe blocked vent safety shutoff switch is a thermal switch. 4) The pushand pull combustion system of claim 1, wherein the blower creates anupstream path of positive pressure in the burner box, while theinduced-draft blower creates a downstream path of negative pressure inthe burner box, and wherein the burner box includes an opening fordecoupling the upstream path from the downstream path by maintainingatmospheric pressure in the burner box. 5) The push and pull combustionsystem of claim 4, wherein the opening is sized relative to the volumeof the burner box to determine the effectiveness of the decoupling. 6)The push and pull combustion system of claim 1, wherein the gas valveassembly meters gas into a premix blower and a premix motor draws airinto the premix blower, the air and gas mixing in the premix blower toproduce the lean gas/air mixture, the premix blower pushing the leangas/air mixture into the burner box. 7) The push and pull combustionsystem of claim 1, wherein the gas valve assembly meters gas into aburner mixing tube and an air blower draws air into the burner mixingtube, the air and gas mixing in the burner mixing tube to produce thelean gas/air mixture, the air blower pushing the lean gas/air mixtureinto the burner box. 8) A furnace with a push and pull combustionsystem, comprising: a premix chamber capable of mixing gas and air toproduce a lean gas/air mixture; a gas valve assembly coupled to thepremix chamber and capable of metering gas into the premix chamber; aburner box downstream of the premix chamber; an igniter associated withthe burner box and adapted to ignite the lean gas/air mixture to producecombustion products; a blower coupled to the premix chamber and adaptedto draw air into the premix chamber, wherein air and gas mix to producea lean gas/air mixture, the blower then pushing the lean gas/air mixtureinto the burner box; a heat exchanger downstream of the burner box; aflue pipe downstream of the heat exchanger; an induced-draft blowercoupled in-between the flue pipe and the heat exchanger and adapted topull the combustion products through the heat exchanger, the flue pipe,and out into the atmosphere; and a cabinet housing therein the burnerbox, the gas valve assembly, the premix chamber, the heat exchanger, theblower, the induced-draft blower, and the flue pipe. 9) The furnace ofclaim 8, wherein the burner box includes an opening and a blocked ventsafety shutoff switch is mounted over the opening, the blocked ventsafety shutoff switch adapted to make thermal contact with fluid flowingout of the opening and sense leakage of combustion products out of theburner box. 10) The furnace of claim 9, wherein the blocked vent safetyshutoff switch is a thermal switch. 11) The furnace of claim 8, whereinthe blower creates an upstream path of positive pressure in the burnerbox, while the induced-draft blower creates a downstream path ofnegative pressure in the burner box, and wherein the burner box includesan opening for decoupling the upstream path from the downstream path bymaintaining atmospheric pressure in the burner box. 12) The furnace ofclaim 8, wherein the gas valve assembly meters gas into a premix blowerand a premix motor draws air into the premix blower, the air and gasmixing to produce the lean gas/air mixture, and the premix blowerpushing the lean gas/air mixture into the burner box. 13) The furnace ofclaim 8, wherein the gas valve assembly meters gas into a burner mixingtube and an air blower draws air into the burner mixing tube, the airand gas mixing to produce the lean gas/air mixture, and the air blowerpushing the lean gas/air mixture into the burner box. 14) A method forcontrolling combustion emission for a furnace, comprising the steps of:metering gas into a premix chamber; drawing air into the premix chamber;mixing gas and air within the premix chamber to produce a lean gas/airmixture; pushing the lean gas/air mixture into a burner box; ignitingthe lean gas/air mixture within the burner box to produce combustionproducts; and pulling the combustion products out of the burner box. 15)The method of claim 14, wherein the air is drawn by a premix motor intoa premix blower and gas is metered by a gas valve assembly into thepremix blower, the air and gas mixing in the premix blower to producethe lean gas/air mixture, the lean gas/air mixture being pushed by thepremix blower into the burner box. 16) The method of claim 14, whereinair is drawn by an air blower into a burner mixing tube and gas ismetered by a gas valve assembly into the burner mixing tube, the air andgas mixing in the burner mixing tube to produce the lean gas/airmixture, the lean gas/air mixture being pushed by the air blower intothe burner box. 17) The method of claim 14, wherein the combustionproducts are pulled out of the burner box by an induced-draft blower.18) The method of claim 14, wherein the lean gas/air mixture is pushedinto the burner box by a blower. 19) The method of claim 14, furthercomprising the step of ensuring negative pressure in the burner box bymounting a blocked vent safety shutoff switch relative to an opening ofthe burner box, the blocked vent safety shutoff switch detecting leakageof combustion products out of the burner box. 20) The method of claim14, wherein pushing the lean gas/air mixture into the burner box createsan upstream path of positive pressure in the burner box and pulling thecombustion productions out of the burner box creates a downstream pathof negative pressure in the burner box, and wherein the burner boxfurther includes an opening for maintaining atmospheric pressure in theburner box and decoupling the upstream path from the downstream path.